The objectives of this research proposal are to assess the extent to which consumption of different sources of hydrogenated fat relative to unhydrogenated oil or butter alters plasma lipoprotein concentrations and measures of lipid metabolism. Forty subjects (20 male, 20 female) aged > 50 years with LDL cholesterol concentrations > 130 mg/dl will be fed each of 5 diets for 8 week periods. The baseline diet will consist of 36% of energy as fat (15% saturated, 15% monosaturated, 6% polyunsaturated) and 160 mg cholesterol/1000 kcal. The experimental diets contain 30% energy as fat, 2/3 of which will be derived from each of the following: 1) unhydrogenated liquid soybean oil, 2) soybean oil margarine in tub form, 3) commercial shortening, and 4) butter in a randomized double blind, cross-over design. With the exception of the experimental fat, all other foods in the reduced fat diets will be identical. The Specific Aims of the study are to assess the impact of consuming diets enriched in hydrogenated and other fats on a) plasma lipids and lipoprotein concentrations, b) apolipoproteins A-1 and B and Lp(a) concentrations, c) parameters related to HDL cholesterol [particle size, composition, subfraction distribution (HDL2 and HDL3, and HDL with and without A-II)], d) susceptibility of LDL to oxidation, e) activities of lecithin cholesterol acyltransferase (LCAT) and cholesterol ester transfer protein, and f) rates of endogenous cholesterol synthesis. Although the consumption of trans-fatty acids or hydrogenated fat has consistently been shown to elevate concentrations of total and LDL cholesterol, the effects on HDL-cholesterol and Lp(a) are inconsistent, especially when the fats were consumed at moderate levels. In addition, little is known about the mechanisms by which trans-fatty acids increase total and LDL cholesterol levels or how they may alter the atherogenecity of lipoprotein subfractions. In the proposed study, the interventions will employ commonly used hydrogenated fats with a wide range of trans-fatty acid levels (1.5-9.8%). The impact will be assessed within the context guidelines currently recommended for individuals with moderately elevated plasma levels for which dietary modification is often the first approach to treatment. The investigators state that the results of the study may lead to improved public health recommendations concerning trans-fatty acid and hydrogenated fat intake.